1. Field of the Invention
This invention relates to lubricated surfaces. More particularly, the invention relates to a coating for a surface which is lubricious and biocompatible when in contact with a body fluid, and to a method for preparing same.
2. Background
Many articles, devices and products require a lubricated surface. In the medical instrumentation and diagnostic field, simple sensing devices such as, for example, thermometers and needles, or electrode components of complex monitoring apparatuses, must be inserted into a body cavity or through the skin and at a later time withdrawn. Patient treatment often includes catheterization procedures or nutrition delivery systems, most of which involve invasive techniques. In all such cases, effective lubrication which is stable throughout both the insertion and withdrawal stages of the procedure contributes greatly to patient comfort.
Many medical devices are fabricated from glass or polymeric materials such as polypropylene, polyvinyl chloride, polytetrafluoroethylene and polyurethane. Such materials are for the most part inherently nonlubricious. A variety of approaches to introduce lubricity have been advanced. Simple coatings of lubricants such as mineral oils or silicones to glass or polymeric surfaces are generally unsatisfactory because the surface energy is too low and the lubricant tends to migrate or "bead." A method to overcome migration of silicone lubricants is described by Williams et al. in U.S. Pat. No. 4,767,414. A surface to be lubricated is coated with silicone oil and both the surface and oil are subjected to an ionizing plasma.
Spielvogel et al., in U.S. Pat. No. 4,720,521 teaches adherence of a lubricating composition to a surface. The composition includes a polysiloxane lubricant entrapped in a mixture of a plurality of reactive silicone components which, on curing, adhere to the surface.
Thermoplastic polyurethanes prepared from polyisocyanates, high molecular weight polyetherglycols, and low molecular weight diols and diamines as chain extenders are conventionally referred to as polyetherurethanes, and this term, will be used in this disclosure for polyurethanes having a polyether backbone.
Polyetherurethane compositions develop microdomains conventionally termed hard segment domains and soft segment domains and are often referred to as segmented polyurethanes. They are (AB)n type block copolymers, A being the hard segment and B the soft segment. The hard segment domains form by localization of the portions of the copolymer molecules which include the isocyanate and extender components whereas the soft segment domains form from the polyether glycol portions of the copolymer chains. The phase seperated microdomain structure forms if the hard segments of polyetherurethane chain are a certain size. A long hard segment promotes the phase separated microdomain structure. Conversely, non extended formulations (those lacking an extender) have very short hard segments and minimum phase seperated microdomain structure. The hard segment is crystalline and provides physical crosslinking and reinforcement. The polyether glycol soft segment is mostly in a rubbery state and provides elasticity. Therefore, polyetherurethanes are thermoplastic elastomeric materials. A wide range of physical properties can be obtained by altering the relative ratios of the hard and soft segments. The elasticity, toughness and other desirable properties of polyetherurethanes are the result of their phase seperated microdomain structure.
Elastomeric segmented polyurethanes have particular advantages for fabrication of medical devices, as discussed by Gilding et al. in U.S. Pat. No. 4,062,834 but have limited inherent lubricity. Micklus et al. in U.S. Pat. No. 4,100,309 teaches a lubricious polyurethane-polyvinylpyrrolidone (PVP) interpolymer coating which may be applied to a polymeric article by dipping the article into a solvent solution of polyurethane and a polyisocyanate to give an isocyanate-containing prepolymer on the article surface and dipping the prepolymer-coated article into a solution of PVP.
In U.S. Pat. No. 4,373,009 to Winn, a substrate surface is primed with a polyisocyanate as shown by Micklus et al., and the isocyanate groups are covalently bonded to active hydrogens of a hydrophilic copolymer, such as a copolymer of PVP and acrylamide. A coating which is stable and resistant to removal, in contrast to prior art coating, is claimed.
U.S. Pat. No. 4,642,267 to Creasy et al. describes lubricious coatings which are alloys or blends of PVP and polyurethanes lacking both free isocyanate groups and chain extenders.
Although the above disclosures have advanced the art of rendering surfaces lubricious, there remains a need for a coating which is instantly lubricious, easily applied and strongly adherent so as to remain on the substrate to which it is applied with no tendency to wash off or separate as solid flakes on prolonged contact with liquids.